With the assistance of Dr. Thomas Hulsey, epidemiologist and co-investigator of this application, sample size calculations were made. All outcome markers are ratio-scaled and normally distributed. Because of the possibility of premature delivery and patient attrition during this study, enrollment of additional subjects over that minimally needed, will provide a cost effective opportunity to conduct additional analyses examining changes in vitamin D associated with diet, seasonality, and maternal medical complications. As one of the major goals of this study is to explore maternal health disparities by ethnicity, the two supplemented groups (400 and 4,400 IU/day) will be balanced by ethnicity (equal numbers of Caucasian, African American, and Hispanic). This sampling distribution will be accomplished by stratified randomization. This sampling frame was selected to provide: (1) sufficient numbers to examine associations with covariates; (2) the volume of initial and follow up samples will be manageable by our laboratory; (3) over-samples to compensate for losses to follow up; and, (4) stabilizes the sophisticated statistical analysis techniques (repeated measures).